Low temperature liquefied gas tanker ship equipped with membranous vessels

ABSTRACT

A tanker ship construction equipped with low temperature liquefied gas tanks having membranous vessels for containing low temperature liquefied gases. The tank is mounted within a hold space prepared in the ship hull. The tank includes an outer box of a steel structure and a heat insulating layer. The outer box has side walls and a bottom adapted to be just strong enough to hold the whole shape thereof for the convenience of the construction and assembly, but not strong enough to support the inner pressure applied by the low temperature liquefied gases loaded in the membranous vessel. The box also has a roof adapted to form by itself a roof portion of the hull, whereby the construction of the tank as well as the assembling thereof into the hull is made substantially easier and the period of construction of the tanker ships is substantially shortened.

Yamamoto [111 3,820,491 [4 June 28, 1974 LOW TEMPERATURE LIQUEFIED GAS TANKER SHIP EQUIPPED WITH MEMBRANOUS VESSELS [75] Inventor: Katsuro Yamamoto, Tokyo, Japan [73] Assignee: Bridgestone Liquefied Gas Company, Ltd., Tokyo, Japan [22] Filed: Mar. 27, 1972 [21] Appl, No.: 238,347

[30] Foreign Application Priority Data FOREIGN PATENTS OR APPLICATIONS I 921,696 3/1963 Great Britain 114/74 A Primary Examiner-Trygve M. Blix Assistant Examiner-Stuart M. Goldstein Attorney, Agent, or FirmWoodhams, Blanchard & Flynn [5 7] ABSTRACT A tanker ship construction equipped with low temperature liquefied gas tanks having membranous vessels for containing low temperature liquefied gases. The tank is mounted within a hold space prepared in the ship hull. The tank includes an outer box of a steel structure and a heat insulating layer. The outer box has side walls and a bottom adapted to be just strong enough to hold the whole shape thereof for the convenience of the construction and assembly, but not strong enough to support the inner pressure applied by the low temperature liquefied gases loaded in the membranous vessel. The box also has a roof adapted to form by itself a roof portion of the hull, whereby the construction of the tank as well as the assembling thereof into the hull is made substantially easier and the period of construction of the tanker ships is substantially shortened.

1 Claim, 2 Drawing Figures ,PATENIEDJUHZB 1914 $820,491

sum 1 or 2 mmnmum m4 sum 2 or 2 FIG. 2

LOW TEMPERATURE LIQUEFIED GAS TANKER SHIP EQUIPPEI) WITH MEMBRANOUS VESSELS BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to the construction of low temperature liquefied gas tanker ships for transporting low temperature liquefied gases such as petroleum gases which are in a gaseous state at room temperature and can be liquefied under atmospheric pressure. More particularly, this invention relates to low temperature liquefied gas tanker ships equipped with low temperature liquefied gas tanks of a membrane type, wherein said tanks are composed of membranous vessels made of a low temperature resisting material and confined in hold spaces to be supported by the walls thereof via a heat insulatinglayer of compression resisting property, said walls of the hold spaces being provided by inner walls of the hull or bulkheads. r

2. Description of the Prior Art As a method of constructing low temperature liquefied gas tanker ships including the membranous tanks of the abovementioned structure, it has been proposed to construct the membranous vessels and the hull separately, the hull being adapted to provide hold spaces in which the membranous vessels are positioned, and thereafter to assemble the membranous vessels and the hull together by inserting the membranous vessels into the hold spaces so as to shorten the period of construction of the tanker ships or the period of occupying docks for the construction of the tanker ships.

However, this conventional method has a drawback that, since the membranous vessel has no rigidness as a whole structure, it is a very difficult work to mount the membranous vessel in the hold space by suspending the membranous vessel at its top portions and lowering it into the hold space. Furthermore, according to the conventional method, the deck structure provided over and adapted to cover a roof portion of the vessel must be constructed after the vessel has been mounted in the hold space, whereby the advantage of shortening the period of construction of the tanker ship is minimized. Furthermore, the mounting of various equipments such as loading and unloading pipes for low temperature liquefied gases requires an additional period to be expended as usual after the construction of the deck has been completed. Therefore, the conventional method could not substantially shorten the overall period of construction of the tanker ships equipped with the membranous tanks for carrying low temperature liquefied gases.

SUMMARY OF THE INVENTION Therefore, it is the main object of this invention to provide low temperature liquefied gas tanker ships equipped with low temperature liquefied gas tanks of a membrane type, whereby the period of construction is substantially shortened. I

Another object of this invention is to provide tanker .ships of' the abovementioned structure, whereby the adapted to provide hold spaces in which said membra-.

nous vessels are positioned, and thereafter assembling the membranous vessels and the hull together in a manner of mounting the membranous vessels within the hold spaces, characterized in that the membranous vessel is constructed as a tank assembly including an outer box of a steel structure and a heat insulating layer of compression resisting property provided between the outer box and the membranous vessel, said outer box being adapted to have a bottom and side walls substantially made of steel plate having thickness large enough to hold the whole shape of the tank assembly but not enough to support the inner pressure applied by the low temperature liquefied gases loaded in the membranous vessel and a roof having high strength and rigidity enough to support said inner pressure, wherein the roof of the tank assembly may preferably be adapted to form .the roof portion of the hull or generally deck when the tank assembly has been mounted in the hold space of the tanker ship.

Since the tank assembly has the outer box providing rigidness great enough to hold the whole shape of the assembly and the roof structure having strength and rigidness great enough to form the roof portion of the hull, the assembly can be very easily suspended by being carried at the roof structure, whereby the tank assembly can be very easily inserted into the hold space prepared in the hull to be mounted therein. Since the roof of the assembly is adapted to provide by itself the roof portion of the hull or generally deck, no additional work of constructing the roof portion of the hull or deck is required after the completion of the mounting of the membranous vessels, whereby the period of construction of the tanker ship is substantially shortened.

The tank assembly having the outer box made of steel plate providing rigidness high enough to hold the whole shape of the assembly and adapted to be suspended by being carried at the rigid roof structure thereof is constructed much easier than a single structure made only of the membranous vessel. When the tank assembly has been mounted within the hold space, the outer box is firmly backed up by the walls of the hold space pro vided by the hull or the bulkhead, whereby when the I membranous vessel was loaded with low temperature liquefied gases, the inner pressure applied by the liquefied gases is positively supported by the hull structure through the outer box and the heat insulating layer of the compression resisting property provided between the outer box and the membranous vessel. Thus, it is accomplished by this invention to spare much amount of material required for the construction of a tanker ship as compared with such a case that a tank assembly having strength and rigidness high enough to support the inner pressure is preliminarily prepared and mounted into the hull.

According to an additional feature of this invention, the. roof structure of the assembly is beforehand preferably equipped with loading and unloading means such as pipes, pumps, valves, etc., which are usually mounted to the roof structure by way of a dome provided on the deck of the hull. By preparing the loading and unloading means before the assembly is mounted to the hull, it is possible to do highly precise and careful construction of the loading and unloading means as highly precise and careful construction is really required, and furthermore, the overall period of construction of the tanker ship is so much shortened.

BRIEF DESCRIPTION OF THE DRAWING The accompanying drawing is a perspective view showing'a cross section of a low temperature liquefied gas tank assembly (FIG. 1) and a low temperature liquefied gas tank mounted in a tanker ship (FIG. 2) constructed according to this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawing, the tanker ship comprises a dual-walled hull 1 having an inner side wall 2 and an inner bottom plate 3, and a longitudinal bulkhead 4 and a transverse bulkhead (not shown), wherein a hold space 5 is defined by the inner side wall 2, the inner bottom plate 3 and the bulkhead 4 as a cavity open at the upper portion thereof.

A tank assembly of the membranous vessel designated by reference numeral 6 as a whole and adapted to be mounted in the hold space 5 is composed of a membranous vessel 7 made of thin plate of a low temperature resisting material such as nickel steel, stainless steel or aluminum and a supporting structure 8 provided at the outside of the membranous vessel 7 in a manner for enclosing the vessel 7. In this embodiment, the membranous vessel 7 is actually formed of two membranous vessels 7a and 7b laid one over the other so as to provide a double layered membranous vessel, wherein the outer one is adapted to perform as a secondary barrier wall in case that a leakage has occurred at the inner membranous vessel. The supporting structure 8 comprises an outer box 9 of a steel structure substantially made of steel plate and a heat insulating layer 12 35 of compression resisting property, such as a combination of wooden frames and heat insulating material of indeterminate form 11, the latter filling the spaces formed by the former.

The outer box 9 comprises a bottom plate 13 and side walls 14 made of steel plate having a relatively small thickness which is enough to support the whole shape of the tank assembly 6 but not enough to support the inner pressure applied by the low temperature liquefied gases loaded in the membranous vessel 7 and a roof portion 15 having high strength and rigidity enough to support the inner pressure of the vessel 7.

The tank assembly 6 is constructed separately from the hull 1. During this separate construction of the tank assembly 6, the roof portion 15 is equipped with a dome 16 adapted to be closed by a cover 17 and loading and unloading means such as loading and unloading pipes 18 for liquefied gases, a gas pipe 19, valves 20 and 21, pumps 22 mounted at the lower ends of the pipes 18, a level indicator 23, etc., wherein these loading and unloading means are directly or indirectly mounted to and supported by the cover 17 of the dome 16. The cover 17 is further equipped with a hatchway 24 adapted to be gas-tightly closed and a ladder 25 extending downward from the hatchway for the inspection and maintenance of the tank. The pipes 18 and 19 are extended above the cover 17 therethrough and are connected to horizontal pipe portions 18a and 1911, respectively, which are running over the deck and supported by a stand 26. The tank assembly 6, which has been constructed separately form the hull l and equipped with the loading and unloading means as described above, is suspended by a crane such as floating crane of a large capacity and is lowered into the hold space 5 to be mounted therein.

The process of suspending the tank assembly 6 and mounting it in the hold space 5 is made substantially easier by the fact that the outer box 6 has the rigid roof 15 and the side walls 14 which can hold the whole shape of the tank assembly.

When the tank assembly 6 has been correctly positioned in the hold space 5, edge portions of the roof 15 are firmly connected to the rim members 27 forming the upper open edge of the hold space 5, and the horizontal pipe portions 18a and 19a are connected to the corresponding pipe portions belonging to adjacently mounted tank assemblies.

Furthermore, the tank assembly may preferably be equipped with cantilevers 28 mounted to bottom end portions of the dome l6 and adapted to support the roof portion of the membranous vessel 7. By the provision of these cantilevers 28, the loading and unloading pipes 18 can be firmly supported against swaying via wires 29 extended between the free ends of the cantilevers 28 and the pipes 18, wherein a pair of the pipes 18 are firmly connected with each other as shown in the drawing.

In the low temperature liquefied gas tanker ship shown in the drawing and constructed according to the method of this invention, the inner pressure of the membranous vessel 7 is supported by the hull l and the rigid roof portion 15 of the tank assembly 6. Therefore, it is not necessary that the bottom and side wall portions of outer box 9 are formed to have substantial strength beyond the requirement of holding the whole shape of the tank assembly 6 in the process of assembly.

Since the roof portion of the tank assembly 6 is prepared to form by itself the roof portion of the hull or generally deck, it is not necessary to expend additional time for the construction of the roof portion of the bull or deck after the mounting of the tank assembly, whereby the period of construction of the tanker is substantially shortened.

From the foregoing, it will be appreciated that this invention provides a very improved method of constructing the low temperature liquefied gas tankers equipped with the membranous vessels whereby the portions operating as the hull and the portions operting as the low temperature liquefied gas tanks are reasonably separated regarding the process of construction so as to reduce the amount of the construction which necessitates the occupation of docks and to substantially shorten the overall period of construction of the low temperature liquefied gas tanker ships equipped with the membranous vessels.

I claim:

1. A method of constructing a tanker ship equipped with a low temperature liquefied gas tank of the membrane type, comprising the steps of:

constructing the hull of the tanker with said hull being provided with a hold space therein adapted to receive a preconstructed low temperature liquefied gas tank assembly;

constructing a low temperature liquefied gas tank assembly of the membrane type separately from the hull of said tanker ship with said tank assembly having bottom and side wall portions which are strong enough to hold their own shape but are not strong enough to support the internal pressure applied thereto when the tank assembly is loaded with low-temperature liquefied gas; completing said tank assembly by securing to the upper edges of the side wall portions a rigid roof structure which closes said tank assembly and is strong enough to withstand the internal pressure applied thereto by the low temperature liquefied gas which is adapted to be loaded in said tank assembly; and then suspending the preconstructed tank assembly by way of the rigid roof structure, said rigid roof structure structure defines a deck of said tanker ship. 

1. A method of constructing a tanker ship equipped with a low temperature liquefied gas tank of the membrane type, comprising the steps of: constructing the hull of the tanker with said hull being provided with a hold space therein adapted to receive a preconstructed low temperature liquefied gas tank assembly; constructing a low temperature liquefied gas tank assembly of the membrane type separately from the hull of said tanker ship with said tank assembly having bottom and side wall portions which are strong enough to hold their own shape but are not strong enough to support the internal pressure applied thereto when the tank assembly is loaded with low temperature liquefied gas; completing said tank assembly by securing to the upper edges of the side wall portions a rigid roof structure which closes said tank assembly and is strong enough to withstand the internal pressure applied thereto by the low temperature liquefied gas which is adapted to be loaded in said tank assembly; and then suspending the preconstructed tank assembly by way of the rigid roof structure, said rigid roof structure also being strong enough to remain horizontal during said suspending of said preconstructed tank assembly; inserting the suspended tank assembly into the hold space within the hull so that the side and bottom wall portions of the tank assembly are reinforced by portions of the hull; and then permanently securing the rigid roof structure of said tank assembly to said hull so that said rigid roof structure defines a deck of said tanker ship. 